It has become increasingly evident that the class of delayed skin hypersensitivity termed cutaneous basophil hypersensitivity (CBH) (or Jones-Mote reaction) is directly involved in a variety of clinically important situations. It is our long-term goal to characterize the subclasses of regulatory thymic-derived cells responsible for inducing, amplifying, and suppressing these reactions in vivo. We have previously reported that injecting guinea pigs with the small "hapten-like" molecule azobenzenearsonate-N-chloroacetyltyrosine (ABA-T) in induction of CBH reactions to the protein protion of proteins possessing the ABA determinant (ABA-protein conjugates). In contrast, we describe here the second finding that ABA-T injected with complete Freund's adjuvant results in amplifier-cells which greatly augment the degree of CBH sensitization to the protein portion of ABA-protein conjugates. We propose to study the above model to determine the in vivo changes which occur with CBH reactions undergoing suppression or amplication. Secondly, using ABA-modified mitogens and antigens in vivo and in vitro we will analyse and characterize these specific regulatory cells.